Single-use systems are being increasingly realized in the medical or laboratory technology as compact medical functional devices such as cassette systems or blood treatment cassettes in which liquids and gases, in particular medical fluids and blood, are conducted in passages and chambers. If they are provided for a single use, one speaks of disposable cassettes or single-use cassettes.
In most cases, these are hard-part film cassettes. The hard part regularly consists of an injection molding material such as PE, PP, PA, ABS, PMMA, PC or PVC. In it, for example, hose connections, connectors, chambers, channels and alignment devices are embodied. The chambers and channels are usually designed as semi-open, fluid-conducting structures. A film made of material compatible to the hard part (suitable for welding on or gluing to the hard part) seals the semi-open structures and completes them to fully adequate chambers and channels. The film may only be, for example, welded on or glued to the blood treatment cassette at an outer closed or peripheral edge. There also are designs where the boundaries of the chambers and channels, the so-called channel edge bars, are welded on or glued to the film in strip form or over a larger area. In this manner, blood treatment cassettes which already provide a defined fluid conduction prior to being equipped in a treatment machine and after being removed are produced.
Certain areas of the hard part and the film are often deliberately not welded on or glued to each other. These areas may be used as film valves between different fluid-conducting areas. For this purpose, the blood treatment cassette is inserted in the blood treatment apparatus between a door and an actuator-sensor-unit of the blood treatment apparatus, and subsequently by closing the door, the latter is brought into a so-called grouting or pressing position in which the film is grouted or pressed against the hard part, and the blood treatment cassette with the film is coupled in a spatially defined manner to the actuator-sensor-mat of the actuator-sensor-unit. Actuators integrated into the actuator-sensor-mat and actuator-sensor-plate (or unit) may be able to exercise movements through or over the film, by which, for example, pump or valve functions may be realized. Properties of fluids which flow through the blood treatment cassette may be measured by means of at least one sensor optionally provided on the actuator-sensor-plate.
Production or processing problems may however, occur, particularly with blood treatment cassettes in which the films and film valves are welded in such a way that they are flush with the passage edge along the latter.